Organic light emitting diode display device and driving method thereof

Abstract

An organic light emitting diode display device includes a display unit including a plurality of pixels; a data driver applying data voltage to the pixels; and a power supplier including a first power source providing high-level voltage to the anode electrode of organic light emitting diodes and a second power source providing low-level voltage to the cathode electrode of the organic light emitting diodes included in the pixels, in which the power supplier provides the second power source in a sink method at positive voltage, when the threshold voltage of a driving transistor for driving the organic light emitting diodes shifts to a negative. When gate-source voltage of a driving transistor shifts to negative threshold voltage, it is possible to apply the data voltage at positive voltage and to simplify a driving IC, thereby ensuring wide use, by applying voltage of a second power source ELVSS at positive voltage.

What is claimed is: 
     
       1. An organic light emitting diode display device, comprising:
 a display unit including a plurality of pixels; 
 a data driver applying a data voltage to the pixels; and 
 a power supplier including a first power source providing a first-level voltage to an anode electrode of organic light emitting diodes and a second power source providing a second and lower-level voltage to a cathode electrode of the organic light emitting diodes in order to drive the organic light emitting diodes which are included in the plurality of pixels, 
 wherein, when a threshold voltage of a driving transistor electrically coupled to drive the organic light emitting diodes shifts to a negative voltage value, the power supplier adjusts the second power source to become a positive voltage. 
 
     
     
       2. The organic light emitting diode display device of  claim 1 , wherein the power supplier includes a DC-DC converter that converts a first DC voltage of a DC power source into a second DC voltage, provides a first voltage outputted in accordance with the second DC voltage from a non-inverting terminal to the first power source, and provides a second voltage outputted from an inverting terminal to the second power source. 
     
     
       3. The organic light emitting diode display device of  claim 1 , wherein the driving transistor is an n-channel field effect transistor. 
     
     
       4. The organic light emitting diode display device of  claim 3 , wherein the data driver applies the data voltage having a positive voltage lower than a predetermined positive voltage of the second power source. 
     
     
       5. The organic light emitting diode display device of  claim 1 , wherein the power supplier includes a power source voltage shift unit that shifts the second power source to a predetermined positive shift voltage. 
     
     
       6. The organic light emitting diode display device of  claim 5 , wherein the power source voltage shift unit includes:
 a differential amplifier including a non-inverting input terminal where the voltage of the second power source is inputted and an inverting input terminal where the predetermined positive shift voltage is input; 
 a first transistor including a gate electrode electrically connected to an output terminal of the differential amplifier and the first transistor having one of source and drain electrodes electrically connected to the second power source; and 
 a second transistor including a gate electrode electrically connected to another of the source and drain electrodes of the first transistor, and the second transistor having one of source and drain electrodes electrically connected to the second power source and another of the source and drain electrodes electrically connected to a ground line. 
 
     
     
       7. The organic light emitting diode display device of  claim 6 , wherein the power source voltage shift unit further includes a feedback capacitor having one terminal electrically connected to the inverting input terminal of the differential amplifier and another terminal electrically connected to the output terminal of the differential amplifier. 
     
     
       8. The organic light emitting diode display device of  claim 6 , wherein the power source voltage shift unit prevents oscillation in response to a resistor having one terminal electrically connected to the output terminal of the differential amplifier and another terminal electrically connected to the gate electrode of the first transistor. 
     
     
       9. The organic light emitting diode display device of  claim 6 , wherein the first transistor and the second transistor comprise bipolar junction transistors. 
     
     
       10. The organic light emitting diode display device of  claim 1 , wherein the pixel comprises a pixel circuit electrically connected to a first scan line where a first scan signal is applied, electrically connected to a second scan line where a second scan signal is applied, electrically connected to a data line where the data voltage is applied, and electrically connected to a light emitting line where a light emitting signal is applied. 
     
     
       11. The organic light emitting diode display device of  claim 10 , wherein the driving transistor comprises:
 a gate electrode electrically connected to the data line; 
 one of source and drain electrodes electrically connected to the first power source; and 
 another of the source and drain electrodes electrically connected to the anode electrode of the organic light emitting diode. 
 
     
     
       12. The organic light emitting diode display device of  claim 11 , wherein the pixel comprises a switching transistor including a gate electrode electrically connected to the first scan line and the switching transistor having one of source and drain electrodes electrically connected to the data line and another of the source and drain electrodes electrically connected to the gate electrode of the driving transistor. 
     
     
       13. The organic light emitting diode display device of  claim 11 , wherein the power supplier compensates for variations in the threshold voltage of the driving transistor by providing a reference voltage and an initializing voltage to the pixel. 
     
     
       14. The organic light emitting diode display device of  claim 13 , wherein the initializing voltage is set at a voltage value lower than a voltage of the second power source. 
     
     
       15. The organic light emitting diode display device of  claim 13 , wherein the pixel includes:
 an initializing transistor including a gate electrode electrically connected to the first scan line and the initializing transistor having one of source and drain electrodes to which the initializing voltage is transmitted and another of the source and drain electrodes electrically connected to the anode electrode of the organic light emitting diode; 
 a reference potential transistor including a gate electrode electrically connected to the light emitting line and the reference potential transistor having one of source and drain electrodes to which the reference voltage is transmitted and another of the source and drain electrodes electrically connected to a node; 
 a light emitting transistor including a gate electrode electrically connected to the second scan line and the light emitting transistor having one of source and drain electrodes electrically connected to the node and another of the source and drain electrodes electrically connected to the gate electrode of the driving transistor; 
 a first sustain capacitor having one terminal electrically connected to the gate electrode of the driving transistor and another terminal electrically connected to the node; and 
 a second sustain capacitor having one terminal electrically connected to the node and the other terminal electrically connected to another of the source and drain electrodes of the initializing transistor. 
 
     
     
       16. The organic light emitting diode display device of  claim 15 , wherein appliances of the first scan signal and the second scan signal have a time difference of at least two (2) horizontal periods. 
     
     
       17. A method of driving an organic light emitting diode display device, the method comprising:
 when a threshold voltage of a driving transistor for driving an organic light emitting diode shifts to a negative voltage value, 
 providing a high-level voltage of a first power source to an anode electrode of the organic light emitting diode; 
 providing a low-level voltage of a second power source, which is a predetermined positive shift voltage, to a cathode electrode of the organic light emitting diode; and 
 writing data to the organic light emitting diode by applying a positive data voltage which is set at a lower level compared to the low-level voltage of the second power source to a gate electrode of the driving transistor. 
 
     
     
       18. The method of  claim 17 , wherein the driving transistor is an n-channel field effect transistor. 
     
     
       19. The method of  claim 17 , wherein the predetermined positive shift voltage is determined in accordance with a magnitude of the threshold voltage of the driving transistor shifting to the negative voltage such that the range of the data voltage is maintained to be within a positive voltage value range. 
     
     
       20. The method of  claim 17 , wherein the voltage of the second power source is generated by the predetermined positive shift voltage inputted to an amplifier.